Dimension-hop may allow neutrinos to cheat light speed
A CERN experiment claims to have caught neutrinos breaking the universe’s most fundamental speed limit. The ghostly subatomic particles seem to have zipped faster than light from the particle physics laboratory near Geneva, Switzerland, to a detector in Italy.
Fish that physics textbook back out of the wastebasket, though: the new result contradicts previous measurements of neutrino speed that were based on a supernova explosion. What’s more, there is still room for error in the departure time of the supposed speedsters. And even if the result is correct, thanks to theories that posit extra dimensions, it does not necessarily mean that the speed of light has been beaten.
“If it’s true, it’s fantastic. It will rock the foundation of physics,” says Stephen Parke of Fermilab in Batavia, Illinois. “But we still have to confirm it.”
Neutrinos are nearly massless subatomic particles that are notoriously shy of interacting with other forms of matter. An experiment called OPERA (Oscillation Project with Emusion tRacking Apparatus) sent beams of neutrinos from a particle accelerator at CERN to a detector in the Gran Sasso cavern in Italy, 730 kilometres away.
The neutrinos arrived 60 nanoseconds sooner than they would have if they had been travelling at the speed of light, the team says.
If real, the finding will force a rewrite of Einstein’s theory of special relativity, one of the cornerstones of modern physics (and a theory whose predictions are incorporated into the design of the accelerators at CERN). “It’s not reasonable,” says theorist Marc Sher of the College of William and Mary in Williamsburg, Virginia.
One problem is that the CERN result busts the apparent speed limit of neutrinos seen when radiation from a supernova explosion reached Earth in February 1987.
Supernovae are exploding stars that are so bright they can briefly outshine their host galaxies. However, most of their energy actually streams out as neutrinos. Because neutrinos scarcely interact with matter, they should escape an exploding star almost immediately, while photons of light will take about 3 hours to get out. And in 1987, trillions of neutrinos arrived 3 hours before the dying star’s light caught up, just as physicists would have expected.
The recent claim of a much higher neutrino speed just doesn’t fit with this earlier measurement. “If neutrinos were that much faster than light, they would have arrived [from the supernova] five years sooner, which is crazy,” says Sher. “They didn’t. The supernova contradicts this [new finding] by huge factors.”